Definition
A NOTAM and aeronautical contraction meaning 'below,' used to indicate that something is at a lower altitude, level, or position than a stated reference.
Plain English
BLW is shorthand for 'below.' It tells you that whatever is being described is lower than the altitude or point mentioned.
Context Anchor
Seen in NOTAMs—official notices about temporary or important flight information—and other abbreviated aviation text where space is limited.
Derivation
BLW is a shortened written form of below, made by leaving out the vowels. Recognizing it as the compact form of below helps you read abbreviated notices without stopping on the letters.
Why Pilots Care
NOTAMs and weather reports are dense with contractions. Reading BLW correctly the first time prevents misreading altitude information that may affect route, terrain clearance, or icing layers.
Intuition Check
BLW does not mean behind or before. In this context, it means lower than the stated reference.
Example Sentence 1
The NOTAM reported moderate turbulence BLW 8,000 feet along the route.
Example Sentence 2
The controller advised traffic was BLW our assigned altitude.